Complete config migration cleanup

Retire legacy files and migration fixtures, move runtime state out of the repository, and migrate Tree-sitter and textobjects to their Neovim 0.12-compatible main branches.

README.md

@@ -4,6 +4,9 @@ Living reference for session management, keymaps, commands, and plugin-specific
 
 The active runtime is Neovim 0.12.6 through `~/.local/bin/nvim`. Neovim 0.11.5 remains available at `/opt/neovim/nvim-linux-x86_64/bin/nvim` for emergency rollback; the config starts there with 0.12-only native completion and Undotree disabled.
 
+Persistent undo files are stored outside this repository in
+`stdpath('state')/undo` (normally `~/.local/state/nvim/undo`).
+
 ## Session Management
 
 Session support is automatic but user-controlled:
@@ -274,17 +277,22 @@ Buffer-local keymaps available when inside a git repository:
 
 ### Treesitter `lua/plugins/treesitter.lua`
 
+The Neovim 0.12-compatible `main` branches are used for both nvim-treesitter
+and nvim-treesitter-textobjects. Highlighting and incremental selection use
+Neovim's native APIs; textobjects use explicit plugin mappings. Parser builds
+require `tree-sitter-cli` 0.26.1 or newer (`tree-sitter --version`).
+
 #### Keymaps
 
 ##### Incremental selection
 
 | Key | Description |
 | --- | --- |
-| `+` | Initialize/expand selection |
+| `+` | Initialize/expand selection to the parent node |
 | `g+` | Expand to scope |
-| `-` | Shrink selection |
+| `-` | Shrink selection to the child node |
 
-##### Textobject selection (`select.keymaps`)
+##### Textobject selection
 
 | Key | Target |
 | --- | --- |
@@ -295,7 +303,7 @@ Buffer-local keymaps available when inside a git repository:
 | `al` / `il` | Loop outer / inner |
 | `a/` | Comment outer |
 
-##### Textobject movement (`move` mappings)
+##### Textobject movement
 
 | Key | Action |
 | --- | --- |